The present invention relates to a developing device for image forming equipment and, more particularly, to a developing device of the type having a toner tank made up of a tank portion storing a toner and a toner supply portion contiguous with one side of the tank portion for supplying the toner from the tank portion to a developing section which includes a developing roller.
A developing device of the type described is conventional and incorporated in an electrophotographic copier, facsimile transceiver, laser printer or similar image forming equipment. Generally, to promote easy toner supply from a toner tank to a developing section, the toner tank should preferably be disposed above the developing section in which a developing roller is located to face a photoconductive element. In practice, however, the toner tank and developing section often have to be arranged such that their bottoms are positioned at the same level or height for space and design reasons. Even with such an arrangement, it is necessary to supply the toner from above the developing section and, for this purpose, a toner supply portion of the tank is usually located at one side of and above a tank portion of the tank. An agitator is disposed in the tank portion and rotated to sweep up the toner from the tank portion to the toner supply portion. The agitator is rotated while urging itself against the inner periphery of the tank portion due to the elasticity of an elastic member affixed to the end of the agitator. The agitator is, therefore, subjected to the resistance of the toner. This brings about a problem that since a shaft on which the agitator is mounted needs an extremely great torque when a great amount of toner exists in the tank portion. Moreover, when a projection provided in the toner supply portion for catching the toner swept up by the agitator is located at a higher level than the shaft, the conveying force acting on the toner sharply decreases at the position of the projection. It follows that the position of the toner supply portion is somewhat limited to in turn limit the design freedom of the image forming equipment.